The invention relates to a device for storing and displaying graphic information.
Display and processing of information in the form of graphic data, e.g. diagrams, curves, drawings, etc. are becoming increasingly important, partly in order to render the handling of data processing systems less complicated, and partly because relatively inexpensive equipment is available. However, possible uses are still restricted by the very high storage capacities that are indispensable for storing graphic images.
A graphic display can be made as a matrix-shaped arrangement of numerical values each corresponding to a point of picture field (e.g. screen), and representing a specific grey value or a specific color. For better understanding the following specification discusses only so called digital pictures consisting exclusively of the "colors" and white and being represented by the binary digit Zero and One. A typical representation, e.g. on the screen of a data display device contains 1024.times.1024 of such black-and-white picture elements and requires for storing a digital storage with a capacity of one megabit.
In spite of its high capacity this storage has to have a short access time. On the one hand, the manipulation of graphic data, e.g. an image rotation or a change of the image scale, requires a high number of storage accesses; and on the other, if so-called raster display devices are used, the individual storage cells have to be read out periodically for refreshing the screen.
Another restrictive condition for storage access is the necessity to connect devices with different characteristics. Digital image information, to give an example, can be produced by scanning an original, as e.g. a written document; in that case the memory, as in the refreshing of the screen, is to be sequentially addressed row by row. The same applies when a computer demands access to the storage. Instead of scanning, however, a graphic display can also be produced in so-called vector generators where the individual elements of figures, e.g. straight lines, circles etc. are generated point by point, and which build these patterns bit by bit in the storage with the corresponding point addresses. The speed of image generation is very high and makes high demands to the access rate in the storage.
For financial reasons it has become necessary to return to the usual word or byte-organized digital storages for the realization of storages for image storing. To reduce the effective access time in the reading-out of data blocks it is known from the article "Memory Systems for Image Processing" by van Voorhis and Morrin in IEEE Transaction on Computers, Vol. C-27, Feb. 1979, pages 113 to 125 to build the image storage of several modules and to distribute the data blocks thereon so skillfully that an entire block with its multitude of digital words can be read out in one single storage access. The strategy of distribution of the individual elements of a data block, and the generation of the storage addresses in writing in and reading out, however, is more complicated and demands a complex structure.
It is therefore the object of the present invention to provide a device for storing and displaying graphic information, where data of different original formats are entered, modified, and read out and which, in spite of a storage of low complexity, permits quick storing and retrieval.